Japanese Patent Application Laid-Open No. 3-230767 (1991) discloses a technique of detecting a current in an inverter which converts a DC voltage applied between two DC power supply lines into a three-phase AC voltage. A smoothing capacitor is connected between the DC power supply lines. A shunt resistor is connected to the DC power supply line, at an inverter side relative to the smoothing capacitor. A current flowing in the shunt resistor is detected based on a voltage vector of a voltage outputted by the inverter, and a phase current is obtained by computation using the detected current value.
To operate a power converting apparatus so as to bring an input power factor closer to 1, a configuration is generally adopted in which a PWM converter is connected in series with an inverter.
Japanese Patent Application Laid-Open No. 2002-315343 discloses a technique of detecting a current in a PWM converter which converts a three-phase AC voltage inputted from a power source via an input line into a DC voltage and outputs the resultant DC voltage to between DC power supply lines. A smoothing capacitor is connected between the DC power supply lines. A shunt resistor is connected to the DC power supply line, at a PWM converter side relative to the smoothing capacitor. A current flowing in the shunt resistor is detected based on a voltage vector of a voltage outputted by the PWM converter, and a phase current of an input line is obtained by computation using the detected current value.
The phase current of the input line is used for the control of the PWM converter. Such a control is performed by using only phase information of the three-phase AC voltage. Therefore, it is necessary to detect the amplitude of a power source, in order to monitor a malfunction of the power source such as an instantaneous power failure and a voltage drop. For example, a voltage between the DC power supply lines is detected.
Japanese Patent Application Laid-Open No. 5-056682 (1993), L. wei, T. A. Lipo, “A Novel Matrix Converter Topology with Simple Commutation”, IEEE ISA2001, vol. 3, pp. 1749-1754, 2001, Koji Kato, Jun-ichi Itoh, “Improvement of Waveform for Step-up AC/DC/AC Direct Power Converter”, 2007 Annual Conference of I.E.E. of Japan, Industry Applications Society, pp. 1 to 31, pp. 1-279 to 282 and Takaharu Takeshita, Koji Toyama, Nobuyuki Matsui, “PWM Scheme for Current Source Three-Phase Inverters and Converters”, Journal of IEEJ, D, vol. 116, No. 1, pp. 106-107, 1996 disclose techniques pertinent to the present invention.